Paint Calculator
Find out exactly how many gallons of paint a room needs — accounting for doors, windows, multiple coats, and the ceiling — plus the total cost.
How to Calculate Paint for a Room
Start with the wall area: add the room's length and width, double it, and multiply by the ceiling height — that's 2 × (length + width) × height. Subtract the openings you won't paint, roughly 21 sq ft for each door and 15 sq ft for each window. If you're also painting the ceiling, add length × width. The result is your paintable area.
A gallon of paint covers about 350 square feet in a single coat, so divide your paintable area by the coverage and multiply by the number of coats, then round up to whole gallons. Most jobs need two coats for even color, and primer counts as its own coat. This calculator handles the coats, openings, and ceiling for you and estimates the cost.
Frequently Asked Questions
How much paint do I need for a room?
Find the wall area with 2 × (length + width) × ceiling height, subtract about 21 sq ft per door and 15 sq ft per window, then divide by the paint's coverage (around 350 sq ft per gallon) and multiply by the number of coats.
How many gallons to paint a 12x12 room?
A 12 × 12 room with 9 ft ceilings has roughly 432 sq ft of wall. After subtracting two doors and two windows you need about one gallon per coat, so two coats take about two gallons.
Does one gallon cover two coats?
No. Coverage figures like 350 sq ft per gallon are for a single coat. For two coats you need roughly twice the paint, which this calculator accounts for automatically.
Turn Your Measurements Into a Real Floor Plan
Once you know your dimensions, generate a labeled, to-scale floor plan in seconds — then export it to DXF or build it in 3D. No CAD experience needed.
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